Refrigeration & Air-Conditioning Practice Set-3

May 18, 2021

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1. If a heat pump cycle operates between the condenser temperature of +27°C and evaporator temperature of -23°C, then the Carnot COP will be

0.2

1.2

2. A bootstrap air cooling system has

One heat exchanger

Three heat exchangers

Two heat exchangers

Four heat exchangers

3. The minimum temperature to which water can be cooled in a cooling tower is

Wet bulb temperature of air

Dry bulb temperature of air

Dew point temperature of air

Ambient air temperature

4. The operating pressure for refrigerating units using R-12 as a refrigerant is

8 bar

15 bar

30 bar

2 bar

5. The C.O.P. of a refrigerator working on a reversed Carnot cycle is (where T₁ = Lowest absolute temperature, and T₂ = Highest absolute temperature)

T₁ / (T₂ - T₁)

T₂/ (T₂ - T₁)

(T₂ - T₁)/T₁

(T₁ - T₂)/T₁

6. In a refrigeration system, heat absorbed in comparison to heat rejected is

More for small capacity and less for high capacity

Same

Less

7. The boiling point of ammonia is

-33.3°C

-30°C

-10.5°C

-77.7°C

8. Mass flow ratio of NH₃ in comparison to Freon-12 for same refrigeration load and same temperature limits is of the order of

1: 1

9: 1

1: 9

1: 3

9. In a refrigeration system, the expansion device is connected between the

Compressor and condenser

Condenser and receiver

Receiver and evaporator

Evaporator and compressor

10. When the temperature of the surrounding is higher than the temperature of the body, then the heat loss by convection from the body to the surrounding will be

Zero

Negative

Positive

None of these

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11. Critical temperature is the temperature above which

Water will evaporate

Water will never evaporate

A gas will never liquefy

A gas will immediately liquefy

12. Most thermostatic expansion valves are set for a superheat of

5°C

15°C

20°C

10°C

13. A reversible engine has ideal thermal efficiency of 30%. When it is used as a refrigerating machine with all other conditions unchanged, the coefficient of performance will be

1.33

3.33

4.33

2.33

14. Highest temperature encountered in refrigeration cycle should be

At critical Temperature

Much below critical temperature

Near critical temperature of refrigerant

Above critical temperature

15. Which of the following statement is correct?

(B) The increase in air movement increases the evaporation from the human body.

(A) The human body can lose heat even if its temperature is less than the atmospheric temperature.

(D) Both (A) and (B)

16. In a flooded evaporator refrigerator, an accumulator at suction of compressor is used to

Collect liquid refrigerant and prevent it from going to compressor

Superheat the vapour

Detect liquid in vapour

Collect vapours

17. The atmospheric air at dry bulb temperature of 15°C enters a heating coil maintained at 40°C. The air leaves the heating coil at 25°C. The bypass factor of the heating coil is

0.6

0.67

0.376

0.4

18. The vapour compression refrigerator employs the following cycle

Carnot

Reversed Rankine

Rankine

Reversed Carnot

19. The curved lines on a psychrometric chart indicates

Relative humidity

Dew point temperature

Wet bulb temperature

Dry bulb temperature

20. A human body feels comfortable when the heat produced by the metabolism of human body is equal to the

(B) Heat stored in the human body

(D) Difference of (A) and (B)

(A) Heat dissipated to the surroundings

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21. For obtaining high COP, the pressure range of compressor should be

Any value

Low

High

Optimum

22. The value of C.O.P in vapour compression cycle is usually

Always more than unity

Any one of the above

Equal to unity

Always less than unity

23. Rating of a domestic refrigerator is of the order of

0.1 ton

5 tons

10 tons

40 tons

24. The refrigerant after condensation process is cooled below the saturation temperature before throttling. Such a process is called

Normal cooling

Super-cooling

Sub-cooling or under-cooling

None of these

25. The capillary tube, as an expansion device, is used in

Room air conditioners

Water coolers

All of these

Domestic refrigerators

26. The domestic refrigerator uses following type of compressor

Piston type reciprocating

Centrifugal

Axial

Miniature sealed unit

27. A certain refrigerating system has a normal operating suction pressure of 10 kg/cm gauge and condensing pressure of about 67 kg/cm. The refrigerant used is

Ammonia

Brine

Carbon dioxide

Freon

28. In a lithium bromide absorption refrigeration system

Water is used as a refrigerant and lithium bromide as an absorbent

None of these

Ammonia is used as a refrigerant and lithium bromide as an absorbent

Lithium bromide is used as a refrigerant and water as an absorbent

29. The change in evaporator temperature in a refrigeration cycle, as compared to change in condenser temperature, influences the value of C.O.P.

Equally

Less

Unpredictable

30. Freon group of refrigerants are

Inflammable

Nontoxic and non-inflammable

Non-inflammable and toxic

Toxic

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31. On the pressure-enthalpy diagram, condensation and desuperheating is represented by a horizontal line because the process

Takes place at constant temperature

Takes place at constant pressure

Involves no change in volume

Takes place at constant entropy

32. Cooling water is required for following equipment in ammonia absorption plant

Absorber

Condenser, absorber and separator (rectifier)

Evaporator

Condenser

33. Which of the following is not a desirable property of a refrigerant?

Good electrical conductor

Large latent heat

Low boiling point

High risibility with oil

34. In actual air-conditioning applications for R-12 and R-22, and operating at a condenser temperature of 40° C and an evaporator temperature of 5° C, the heat rejection factor is about

2.15

1.25

5.12

35. The general rule for rating refrigeration systems (excepting for CO₂ system) is to approximate following h.p. per ton of refrigeration

0.5 to 0.8 h.p. per ton of refrigeration

2 to 5 h.p. per ton of refrigeration

0.1 to 0.5 h.p. per ton of refrigeration

1 to 2 h.p. per ton of refrigeration

36. A thermostatic expansion valve in a refrigeration system

Is suitable only for constant load systems

None of the above

Maintains different temperatures in evaporator in proportion to load

Ensures the evaporator completely filled with refrigerant of the load

37. The bank of tubes at the back of domestic refrigerator is

Evaporator tubes

Capillary tubes

Refrigerant cooling tubes

Condenser tubes

38. The freezing point of sulphur dioxide is

-77.7°C

-135.8°C

-56.6°C

-75.2°C

39. Which of the following cycles uses air as the refrigerant?

Bell Coleman

Ericson

Carnot

Stirling

40. The condition of refrigerant after passing through the condenser in a vapour compression system is

Dry saturated vapour

Saturated liquid

Wet vapour

Superheated vapour

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A Demrot is the founder of VideRime Online Learning, a leading engineering website. He did his BE Civil and M.Tech Structure from RGPV University, Bhopal and has been working as an Assistant Professor in a reputed college.

Refrigeration & Air-Conditioning Practice Set-3

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